This invention relates to a magnetic sensor and, more particularly, to a magnetic sensor for detecting a change in a magnetic flux. Such magnetic sensor is generally employed in position detection and in rotational speed detection.
FIGS. 40 to 48 illustrate a related magnetic sensor to which the magnetic sensor of the present invention pertains, and FIGS. 40 to 43 are views illustrating an example of employment of the related magnetic sensor. In the related magnetic sensor 1, reference numeral 2 is a cylindrical magnetic core, 3 is a coil wound between flanges 5 and 6 on a bobbin 4 on the magnetic core 2, 7 is a cylindrical sleeve (a guide portion) integral with the bobbin 4, 8 is a cylindrical permanent magnet, 9 is a spacer disposed on the magnet 8, 10 and 11 are lead out wires drawn from the coil 3, 12 is a tape for securing the lead out wires 10 and 11 on the sleeve 7, and 13 is a terminal disposed at the other end of the sleeve 7 extending through it, at one end of which the lead out wires 10 are wound and electrically connected by means of solder (not shown) for example and, the other end extending into the connector portion 15 of the housing 14 of the magnetic sensor.
The housing 14, which is a resin molded member which surrounds a sensor assembly composed of the magnetic core 2, the coil 3, the magnet 8 or the like of the magnetic sensor, comprises the above-mentioned connector portion 15, a main body portion 16 containing therein the sensor assembly and a mounting bracket 17. The mounting bracket 17 has formed therein a positioning pin 18 and a hole 19 for receiving therein a mounting screw (not shown). The magnetic sensor 1 is secured to a predetermined position with its main body portion 16 inserted into the circular mounting hole 21 formed in the support structure 20, the positioning pin 18 of the mounting bracket 17 inserted into a positioning hole 22 of the support structure 20, and a mounting screw 24 extended through the hole 19 for receiving the mounting screw and thread-engaged with the threaded hole 23 of the support structure 20.
The magnetic sensor 1 is attached and used, as shown in FIG. 40, in a position where the tip of the magnetic core 2 can be positioned to oppose to the tip of the projection 25 of the rotary member 26 which is a signal detecting magnetic plate. In such state, the magnetic flux from the magnet 8 extends through a magnetic circuit including the magnetic core 2, and the projection 25 of the rotary member 26 periodically comes to the position opposite to the tip of the magnetic core 2 depending upon the rotation of the rotary member 26. According to whether or not the projection 25 is at this position, the magnetic reluctance of the magnetic circuit changes, so that the magnitude of the magnetic flux flowing through the magnetic core 2 changes. This change in magnetic flux is converted into voltage by the coil 3 and outputted from the connector 15. In order to concentrate the magnetic flux generated from the magnetic core to improve the position detection accuracy of the magnetic sensor, the tip surface of the magnetic core and the projection 25 of the rotary member 26 are made substantially the same size and the same configuration, the mounting of the magnetic sensor is carefully achieved by means of the positioning pin 18 or the like so that the tip surface of the magnetic core and the projection 25 are positioned in an accurate opposition.
FIG. 43 is a sectional view taken along line A--A of FIG. 40, FIG. 44 is an enlarged view of the portion from which the lead out wire 10 is extended from the bobbin 4 of FIG. 40, and FIG. 45 is a view illustrating the state in which the lead out line 10 is drawn from the bobbin 4 and wired on the sleeve 7.
The bobbin 4 employed in the cylindrical magnetic sensor 1 comprises a winding core 27 (see FIG. 40) on which the coil 3 is wound and two disc-shaped flanges 5 and 6 disposed at each ends of the core, the flange 6 having formed therein lead out ports 28 and 29 for the lead out wires 10 and 11. The lead out ports 28 and 29 are notches spaced apart from each other and extending inwardly in the substantially radial direction from the outer edge of the flange 6. In the illustrated example, the lead out wire 10 enters from the inner end of the lead out port 28, wound and laminated in layers on the bobbin 4 into the coil 3 and extends out from the outer periphery of the coil 3 to be lead out from the outer end of the lead out port 29 as the lead out wire 11. Therefore, as best seen from the figures, the lead out wire 11 extends outwardly from the flange 6 at the radially outside position of the lead out port 29 and extends radially inwardly onto the sleeve 7 and axially extends on the sleeve 7 together with the lead out wire 10 and secured by the tape 12 and finally wound around the terminal 13 at the other end of the sleeve 7.
Thus, since the lead out wire 11 particularly has a portion extending in radial direction, a tensile stress is applied to the lead out wire 11, and since a pressure is applied due to the molten resin during the molding of the resin mold 16 which is a housing, the lead out wire 11 may be broken. Also, the lead out wire 11 passes at the shallow portion of the lead out port 29, so that the lead out wire 11 may come out of the lead out port 29 and dislocated.
The lead out wires 10 and 11 are secured by solder after they are wound around the terminal 13 at the connection portion, but they are easily damaged during the soldering because of burnt or molten bobbin 4 or sleeve 7 by a hot solder or a soldering iron. Also, since the connection portion is disposed within the cylindrical housing main body 16, the connection portion is arranged not to protrude radially outwardly of the bobbin 4. Therefore, the impregnation into a solder bath cannot be employed for the soldering, the soldering iron had to be manually operated, obstacling an automation of the soldering and increasing the cost of the product.
FIG. 45 is a partial plan view of the sensor assembly in which the coil 3 is wound on the bobbin 4 and the wiring of the lead out wires 10 and 11 by the tape 12 is complete. The tape 12 used must be an expensive heat resisting tape which is resistive to a high temperature occurring during the soldering and the resin molding, resulting in one reason that the product cost cannot be decreased. Also, since the wiring operation by means of the tape 12 must be carried out before the winding and soldering to the terminal 13, i.e., immediately after the winding of the coil 3, this operation must be done by a special device only for this purpose or an independent separate step by hands.
FIG. 46 is a schematic sectional view showing the molding die for use in the resin molding step for the related magnetic sensor 1, from which it is seen that the sensor assembly composed of the magnetic core 2, the coil 3, the bobbin 4 (see FIG. 40), the sleeve 7 (see FIG. 40), the magnet 8, the spacer 9 and the like is housed and supported within a cavity 33 defined by the mold dies 30, 31 and 32. That is, the tip of the magnetic core 2 is intimately fitted into the recessed portion 34 formed in the bottom surface of the cylindrical cavity of the lower die 30, the upper end portion which becomes the connector 15 of the terminal 13 is inserted into and held by the die insert 31 and the upper die 32 is placed over them to define the cavity 33, whereby the sensor assembly is held in a predetermined position within the cavity 33.
In the magnetic sensor which employs such the resin molding die, the magnetic core 2 is moved during the resin molding by the pressure of the injected resin and its center line tilts and offsets, causing an unstable output of the magnetic sensor, resulting in the significant decrease of the value of the product. Also, since the terminal 13 is supported by the die insert 31, the terminal is bent by the pressure of the injected resin.
On the other hand, when the signal output from the magnetic sensor is taken out from the lead wires rather than from the terminal 13, the sensor assembly is supported at only one point by the magnetic core 2 within the die cavity 33, the support is unstable and the resin molding operation is difficult.
In order to obtain a stable support of the assembly within the die cavity, it has been proposed to make the recessed portion 34 of the lower die 30 deep and make the projection portion of the magnetic core 2 sufficiently long. However, when the magnetic core 2 has an increased length in the magnetic circuit of the magnetic sensor 1, the magnetic reluctance is accordingly increased and the signal output from the magnetic sensor 1 is decreased. Further, with the elongated projection of the magnetic core 2, its exposed surface is increased, so that magnetic foreign matters such as iron powders or the like is easily attracted to the exposed surface, providing a change in the magnetic circuit of the magnetic sensor 1 and causing the decrease in the signal output and the shift of the signal generating timing.
Also, in the example illustrated in FIG. 47, one portion of the spacer 9 is outwardly extended from the sleeve 7 in the axial direction of the sensor assembly when there may be a restriction in the axial dimension of the completed magnetic sensor. In such case, the abutment area or the contact area between the spacer 9 and the sleeve 7 is small and the stability of the spacer 9 during the resin injection for the resin molding is poor, so that the spacer 9 and the sleeve 7 must be secured by a cyan-system bonding agent for example. If the bonding agent is used, the number of manufacturing steps is increased and the product cost is increased. Further, the injected bonding agent passes through the gap between the sleeve 7 and the spacer 9 to reach between the spacer 9 and the magnet 8 where it forms a thin film of the bonding agent or a non-magnetic gap increasing the magnetic reluctance between the magnet 8 and the spacer 9, causing decrease in the output from the magnetic sensor.
Also, the related magnetic sensor illustrated in FIG. 47 has a sealing function which is provided by, as shown in FIG. 41, the main body portion 16 of the magnetic sensor inserted into the mounting hole 21 formed in the support structure 20 to hermetically seal therebetween. For this purpose, an O-ring 36 for intimately contacting with the inner circumferential surface of the mounting hole 21 of the support structure 20 is placed within a circumferential groove 35 around the housing main body portion 16.
In FIG. 48, a mold die for use in the resin molding step for manufacturing the magnetic sensor having the above-mentioned O-ring 36, wherein the mold die for forming the resin mold 14 which is the housing is arranged to be oriented within the cavity 33 with the axis of the sensor assembly horizontally and with the connector portion 15 downward, and a die insert 38 for the connector 15 is inserted into the lower die 37 and two separable upper dies 39 and 40 are arranged in the lower die 37. The axis of the sensor assembly is horizontally arranged in order not to form an under cut at the circumferential groove 35 in the housing main body portion 16.
When the sensor assembly in which the spacer 9 projects from the sleeve 7 is horizontally placed within the molding die, the spacer 9 comes out of the sleeve 7 much more easily, so that the previously mentioned bonding agent must be used for secure attachment, lowering the handling efficiency and increasing the cost of the manufactured product as well as degrading the sensitivity of the manufactured magnetic sensor.
Further in the resin molding of the magnetic sensor, for the purpose of miniaturizing the magnetic sensor and reducing the diameter of housing main body portion, as shown in FIGS. 40 and 47, the thickness of the housing main body portion 16 is made thin at the portion where the coil 3 is housed and is made particularly thin at the portion of the flanges 5 and 6 of the bobbin 4. In order to obtain such the arrangement, the clearances defined between the mold die for the resin molding and the flanges 5 and 6 are made small. Therefore, during the resin molding, the injected resin is difficult to enter into this clearances and even a cavity due to incomplete resin molding may be generated due to the poor resin flow. In order to improve resin flow, proposition has been made to increase the resin injection speed or to increase the resin molding pressure, for example, another problem of breaking the lead out wires 10 and 11 drawn from the lead out wire ports 28 and 29 (FIG. 43) of the flange 6 of the bobbin 4 because of the pressure of the resin.
Also, with respect to the positioning of the mounting bed or the like relative to the support structure 20, in the magnetic sensor in which the magnetic sensor is positioned by the projection disposed to the mounting bracket with the mounting bracket disposed placed within a plane parallel to the axis of the magnetic sensor and without inserting the main body portion which houses the sensor assembly into the through hole of the support structure, there was a problem that the distance between the tip of the magnetic core and the positioning projection is increased to degrade the positioning accuracy of the magnetic core tip by the positioning projection. Further, when the positioning projection is to be attached to the mounting bracket as an element separate from the mounting bracket, the number of the components is increased and an assembling of the positioning projection to the mounting bracket is necessary which increases the operation steps, increasing the cost of the product manufactured.
Further, as an example of the positioning, the inner diameter of the through hole for receiving therein screws of the mounting bracket may be made slightly greater than the outer diameter of the thread portion (not shown) of the mounting screw and the mounting screw may be inserted into the through hole, whereby the magnetic sensor is positioned and secured. In this case, the dimension allowance of the inner diameter of the through hole must be made small. Therefore, the machining of the through hole is difficult, requiring the use of a machined bush metal or the like, which causes the increase of the manufacturing cost.
This invention has been made to solve the above-discussed problems of the related magnetic sensor to which the present invention pertains and has as its object the provision of the magnetic sensor which can be easily manufactured at low cost and has a high accuracy and reliability.